Add paths.buffer and PathConfig; rename import→imports with list support

[cweniger]

Summary

• Adds paths.buffer config key to redirect buffer snapshot storage to a separate volume (e.g. HPC scratch), mirroring the existing paths.samples pattern
• Introduces PathConfig dataclass to validate cfg.paths against a typed schema, consistent with how BufferConfig validates cfg.buffer
• Renames paths.import → paths.imports: list[str] — avoids the Python keyword clash and supports multiple search directories prepended to sys.path in Ray workers
• Renames model_path → import_dirs throughout DeployedGraph, NodeWrapper, MultiplexNodeWrapper

Motivation

Buffer snapshots can be large (grows with max_samples × field_size × adaptive_rounds) and should land on fast scratch storage, not alongside model checkpoints and configs on persistent storage. paths.buffer gives users independent control over where snapshots land.

PathConfig brings cfg.paths in line with the rest of the config: typed, validated, with unknown-key rejection via OmegaConf structured config merge.

imports as a list allows specifying multiple module search directories, which was not possible with the old scalar import key.

Migration

Before	After
paths.import: "."	paths.imports: ["."]

Test plan

• Run falcon launch with no paths.buffer set — snapshots land in {run_dir}/buffer/snapshots/ as before
• Run with paths.buffer: /scratch/myproject — snapshots redirect correctly
• Run with paths.imports: [".", "../shared"] — both dirs appear in sys.path in workers
• Config with unknown key under paths: raises OmegaConf error

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 20.58824% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 9.72%. Comparing base (a20f1c7) to head (1785b5d).

Files with missing lines	Patch %	Lines
falcon/cli.py	0.00%	18 Missing ⚠️
falcon/core/deployed_graph.py	0.00%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main     #87      +/-   ##
========================================
+ Coverage   9.61%   9.72%   +0.11%     
========================================
  Files         33      33              
  Lines       4141    4154      +13     
========================================
+ Hits         398     404       +6     
- Misses      3743    3750       +7     

Flag	Coverage Δ
unit	9.72% <20.58%> (+0.11%)	⬆️

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